The present invention relates to a process for recovering metals from a waste lithium ion battery, particularly a process for recovering copper, aluminum, iron and cobalt, as well as lithium carbonate, from a waste lithium ion battery.
Due to its merits, such as a high electrical energy density, a high working voltage, a long cyclic life and no memory effect, etc., the lithium ion battery has been recognized as a battery system with a high potential for development. Currently, in addition to being widely used in various 3C products, the lithium ion battery is expected to replace batteries of lead acid, Nixe2x80x94Cd and Nixe2x80x94H, etc. and becomes a power source for electric cars. By then, the use of lithium ion batteries will grow in multiples. Therefore, along with an increase on the use of lithium ion batteries, a system for recycling and regenerating waste lithium ion batteries should be developed to solve the problems of contamination and risk associated with the use of lithium ion batteries.
In comparison with a lithium ion primary battery, a lithium ion secondary battery uses a lithium oxide, that has a better stability, as a material for the positive electrode. However, during the process of repetitive charge/discharge, the lithium ion secondary battery still has the occurrence of dendrite of lithium metal. Furthermore, when some material (e.g. LiPF6, LiClO4, LiSO2, LiBF4 etc.) commonly used as an electrolyte of the lithium battery come into contact with air or moisture, these material will generate contamination to the natural environment or cause harm to a person""s safety. Among the lithium ion secondary batteries that have been commercially mass produced, their positive electrode material mainly is an oxide of lithium-cobalt. Due to the fact that only a small amount of cobalt is available in the natural environment and cobalt is a valuable metal in military applications, the metal cobalt has a high economic value for recycling.
However, since the techniques for commercially producing the lithium ion secondary batteries are becoming mature only in the recent decade, patent documents related to the recycling of used or waste lithium ion batteries are made public only in recent years. A known process in recycling a waste lithium ion battery includes calcining the batteries in a high temperature furnace to decompose the organic materials in the battery, smashing and sieving the battery, and separating and purifying valuable metals. These techniques can be divided into a physical selection method and a purification method by chemical dissolution.
Physical Selection Method
Japanese patents JP10074539, JP10158751, JP10223264, JP10330855, JP11242967 use physical selection methods. They are characterized in that a waste lithium battery is pulverized to a particle size of less than 5 mesh (or 3.36 mm), and then separated into different metals by an alternate use of processes, such as sieving, magnetic selection, gravity selection or eddy current, using the particles"" physical properties, such as particle size, magnetic property, specific gravity, and electric property, etc. However, as known to the public, metals separated according to their physical properties do not have a high quality. In addition to a satisfactory result can be reached by using a magnetic selection method to recycle iron, other recycled metals are limited in quality by their nature and can not reach a high quality obtained by other methods, such as a wet metallurgy. The reasons include that many metals do not have a high selectivity by their physical properties (such as aluminum and copper in this system), and absolute values of the magnetic or electric properties of the pulverized metal particles are related to the size thereof.
Purification by Chemical Dissolution
A method of purification by chemical dissolution mainly comprises dissolving the positive electrode material of a lithium ion battery containing a Lixe2x80x94Co oxide, and forming a hydroxide or metal compound with a low solubility by adjusting the pH value to recycle valuable metals. A method disclosed in JP7207349 comprises sieving a waste lithium ion battery, which has received a pre-treatment; dissolving the under size portion with an acid; and directly adjusting the pH value to recycle the metal hydroxides. JP11054159 uses nitric acid to dissolve the positive electrode material, and uses lithium hydroxide to adjust the pH value to recycle the metal hydroxides. JP11185834 uses hydrochloric acid to dissolve the positive electrode material of a waste lithium battery, and adds oxalic radicals into the solution to form a precipitation of cobalt oxalate.
The present invention discloses a process for recovering metals from waste batteries including lithium ion batteries, wherein said waste batteries are calcined and sieved to generate an ash containing metals and metal oxides. Said process comprises the following steps:
a) dissolving said ash with a 3N-6N hydrochloric acid aqueous solution containing sodium chloride;
b) using the dissolved solution formed in step a) as a cathode solution and an aqueous solution of salt or acid as an anode solution, and using a current density of 0.001-0.01 ampere/cm2 to perform a membrane electrolysis in a first electrolysis tank divided into a cathode well and an anode well by a cationic exchange membrane, thereby forming by reduction a copper metal on a cathode in said cathode well, wherein hydrogen ions formed in said anode solution penetrate through said cationic exchange membrane, and combine with the chlorine ions in said cathode solution to form hydrochloric acid;
c) withdrawing said cathode solution from said first electrolysis tank, and applying a diffusion dialysis on said cathode solution, thereby obtaining an aqueous solution of hydrochloric acid and a solution with an elevated pH value, wherein said aqueous solution of hydrochloric acid can be recycled for the use in dissolution in step a);
d) using said solution with an elevated pH value from step c) as a cathode solution and an aqueous solution of salt or acid as an anode solution, and using a current density of 0.01-0.05 ampere/cm2 in a second electrolysis tank divided into a cathode well and an anode well by a cationic exchange membrane to perform a membrane electrolysis, wherein the pH value of said cathode solution is controlled to be over 1.5 during said membrane electrolysis process, thereby forming by reduction a cobalt metal on a cathode in said cathode well,
e) withdrawing said cathode solution from said second electrolysis tank, and adjusting the pH value thereof to 5-7, thereby forming a precipitation of Fe(OH)3 and Al(OH)3;
f) performing a solid/liquid separation on the resulting mixture from step e); and
g) adding a water soluble carbonate into the aqueous solution separated in step f), thereby forming a precipitation of lithium carbonate.
Preferably, step e) of the present invention comprises applying a diffusion dialysis treatment on said cathode solution, thereby obtaining an aqueous solution of hydrochloric acid and a solution with an elevated pH value, and selectively adding sodium hydroxide into said solution with an elevated pH value, wherein said aqueous solution of hydrochloric acid can be recycled for the dissolution in step a).
Preferably, the pH values in step d) and step e) of the present invention are controlled or adjusted by adding sodium hydroxide.
Preferably, the water soluble carbonate in step g) of the present invention is sodium carbonate.
Preferably, the method according to the present invention further comprises smashing said calcined product, and collecting the smashed product passing through a screen of 20-5 mesh during smashing. More preferably, the process according to the present invention further comprises separating said smashed product with a screen of 10-5 mesh, thereby obtaining an under size portion containing the ash containing metals and metal oxides, and a portion remained on the screen.
Preferably, the process according to the present invention further comprises separating iron from the portion remained on the screen by a magnetic selection process. More preferably, the process according to the present invention further comprises separating copper and aluminum from the residue generated after the magnetic selection by an eddy current selection process.
Preferably, said 3N-6N hydrochloric acid aqueous solution containing sodium chloride in step a) of the present invention has a concentration of sodium chloride of 50-300 g/liter.
Preferably, the hydrochloric acid aqueous solution containing sodium chloride in step a) of the present invention has a temperature of 60-100xc2x0 C., and the dissolving process is carried out where 5-20 g of the hydrochloric acid aqueous solution containing sodium chloride is used per gram of said ash.
In addition to incorporating the advantages of a physical selection method and a purification method by chemical dissolution, the process according to the present invention also uses a membrane electrolysis process to recover valuable metals in their metal state. Different from smashing a waste lithium ion battery into fine particles and performing the selection process in the prior art, the process according to the present invention comprises smashing the enclosure of a battery and the Cu/Al foil positive/negative electrode materials, that has been coated with Lixe2x80x94Co oxides or carbon powder, into large fragments of more than 3.36 mm (a screen with 5 mesh or lower), thereby reducing the consumption during the smashing process, and increasing the efficiency in separating the copper and aluminum foils in the eddy current selection process. Furthermore, the present invention uses hydrochloric acid to replace sulfuric acid, that has been used conventionally, and uses a membrane electrolysis system to replace a conventional electrolysis process, thereby greatly increasing the dissolution effect while solving the problem of industrial safety caused by the generation of chlorine gas during an electrolysis process using a hydrochloric acid system. Furthermore, the hydrochloric acid generated in a membrane electrolysis process can be recycled to the dissolution system, thereby forming a close system. This is also a characteristic of the present invention. The process according to the present invention can perform a complete treatment on a whole waste lithium ion battery, and recover almost all of the valuable metals.
Compared to a conventional physical selection method, the invented process recovers metals at a higher quality. Furthermore, a mixture of oxides of lithium and cobalt and ash, which can not be processed by a physical selection method, is treated by dissolution and membrane electrolysis to recover metals therefrom according to the invented process. Therefore, the recovery of metal cobalt can be greatly increased. Furthermore, a conventional chemical dissolution purification method recovers a metal in its metal compound form. Therefore, such a method usually can not handle too many types of metal impurities. Its treatment subject is usually limited to the positive electrode material in a battery. Furthermore, its recovered product is a cheap metal compounds in comparison with pure copper and cobalt metals recovered by the process according to the present invention.